Be careful to always square your buildings. If you use iD-Editor, you can do it by pressing Q. It saves a lot of avoidable work in validation

Make sure to square your buildings. If you use iD-Editor, you can do that by pressing Q. It saves a lot of avoidable work

Make sure to square your buildings when mapping new ones. If you use iD-Editor, you can do that by pressing Q while selecting the building.

I'm only mapping structures that are visible from aerial imagery (usually Esri or Bing, which are embedded into JOSM). You can also see the used background maps in the source tag of the changesets.